The present invention relates to filtration units for laboratory use and more particularly to a reusable filtration unit having a recoverable filter membrane.
A variety of reusable filter units as known in the art are used in various laboratory applications wherein a sample of a liquid is filtered through a filter membrane. The filter membrane is then recovered so that the material collected on the membrane can be inspected or cultured.
Briefly, such reusable units usually include an upper body for receiving the liquid to be filtered, a -ower body for receiving the filtrate, an intermediate member for supporting the filter membrane and a means for locking the three components together and effecting an air tight seal about the filter membrane.
Filtration units of the prior art employ various means to releasably assemble and lock the upper and lower bodies together. For example, in one version, the two bodies are threaded so that one may be screwed into the other. Bayonet locks are also employed and still another version has the mating ends of the upper and lower bodies provided with magnets for holding them together.
In the bayonet and threaded attachments (and to some extent in the magnetic attachment), one of the bodies must be rotated or twisted with respect to the other in order to assemble or disassemble the filter unit. Such an arrangement is not entirely satisfactory as relative rotation of one or another of the bodies during assembly or disassembly may twist, bend or even tear the filter membrane. Damage to the membrane during assembly of the filter unit could result in poor filtration. Damage resulting during disassembly to remove the membrane could result in loss of some portion of the material filtered from the liquid. For these reasons, it is important and preferred that the upper and lower body members be assembled in a manner which avoids application of a shearing or twisting force to the filter membrane and that the filter membrane be inserted and recovered in as flat a condition as possible.
Another disadvantage of the prior art filter units is that the filter membrane is not easily removed from its support plate, particularly when the membrane has been pressed against this plate as during vacuum filtration. For example, in some prior art units the membrane support plate is fixed to the lower body and no provision is made for inserting a tool between the membrane and support plate to facilitate peeling the membrane from the plate. In other prior art units the support plate is removably located in a recess in either the upper or lower body which makes it difficult to separate the filter support plate from the surrounding structure.